Control method for starting diesel engines

ABSTRACT

A control method for starting a diesel engine makes it possible to prevent an excessive increase in fuel injection rate in a low speed rotation range at the time of starting for prevention of occurrence of misfiring and unstable engine rotation, and to prevent occurrence of black smoke by controlling the injection rate according to the engine temperature. For this effect, from the beginning of engine starting to a first engine rotating speed (N 1 ), the control rack is moved in the fuel injection rate reducing direction so that the rack position has a first gradient to correct for an increase in fuel injection rate and, from the first engine rotating speed to a second engine rotating speed (N 3 ) at which the control rack is returned to its position for ordinary control, the control rack is moved in the fuel injection rate reducing direction so that the rack position has a second gradient greater than the first gradient.

TECHNICAL FIELD

The present invention relates to the control of diesel engines at thetime of starting and, more particularly, to the control of a controlrack position for an increase in the amount of fuel at the time ofstarting for improving the startability of the engine.

BACKGROUND ART

In recent years, as a means for coping with regulations of exhaust fromdiesel engines, the development of injection nozzles having smallernozzle orifice diameters and injection pumps having higher pumpingpressure has been promoted to atomize injected fuel more finely.Formerly, in many cases, the startability at a low temperature could beimproved by injecting more fuel by means of a starting increase functionor the like. However, atomization of fuel promotes vaporization of fuelduring the ignition lag period. Therefore, if the amount of injectedfuel is excessively large, the fuel takes a large amount of heat ofvaporization, reducing the temperature in the engine so that misfire canoccur as an effect contrary to the original purpose. There is,therefore, a need for more accurate control of the fuel injection rate.

For example, in an in-line fuel injection pump or the like for dieselengines, the position of a control rack for injection rate adjustment(hereinafter referred to as "rack" or "control rack") of a governor iscontrolled to change the rate of injection of fuel into the engine.However, even when the position of the rack is fixed, the fuel injectionrate is not constant with respect to the engine rotating speed. That is,an ordinary characteristic of an injection pump is such that, as shownin FIG. 6, the fuel injection rate decreases if the engine rotatingspeed becomes lower when the rack position is fixed. This tendency isstronger in a very low engine speed range.

On the other hand, to improve the startability of an engine, it isnecessary to supply the engine with fuel at a rate high enough toachieve such an engine rotating speed that the engine can rotate againstresistance. In a diesel engine using a mechanical governor, therefore,the fuel injection rate is increased in a lower rotating speed range atthe time of starting the engine relative to the fuel injection rate atthe time of ordinary control. In this method, a starting increase modeis set in which the rack position at the time of starting is on the fuelinjection rate increasing side of the rack position at the time ofordinary control, as indicated by the hatched area in FIG. 7, therebyincreasing the fuel injection rate at the time of starting.

This starting increase is effected by using a spring which is called astart spring and which is comparatively weak in tensile force. Between Aand B, after an engine start and before the rotating speed becomes equalto N₁, the rack position is constantly maintained stationary, by beingstopped by a stop mechanism such as a rack cap. The rack positionbetween B and C, from the rotating speed N₁ to the rotating speed N₂, isdetermined by the balance between the tensile force of the start springand the centrifugal force of a fly weight of the governor. However,since the spring force is weak, the rack position changes abruptly toits ordinary control position, by moving in the injection rate reducingdirection with a steep gradient to reduce the amount of startingincrease to zero.

There is another method using an electronic governor for electronicallycontrolling the amount of operation of an actuator for operating thecontrol rack to adjust the fuel injection rate. Also in this case, acontrol mode of increasing the injection rate at the time of starting,as shown in FIG. 8, is adopted. In this starting increase mode, thestarting increase action of the mechanical governor is directly replacedwith the electronic governor, as is apparent from the figure. That is,between a and b, before the engine rotating speed becomes equal to N₁,the rack position is constantly maintained stationary so that the amountof increase is X₀. The rack position is rapidly adjusted between b andc, in which the rotating speed changes from N₁ to N₂, and the amount ofincrease is thereby set to zero at N₂. Such setting is made in almostall cases. The change between b and c of FIG. 8 is called regulation Rand is expressed by

    R={(N.sub.2 -N.sub.1)/N.sub.1 }×100(%)               (1)

The value of the regulation R is ordinarily 20% or less.

However, considering the points described below, it cannot be said thatthe setting of the above-described conventional starting increase modeis optimal and effective in sufficiently improving the startability. Inthe conventional starting increase mode, as shown in FIG. 7 or 8, therack position is constantly maintained stationary between A and B orbetween a and b. However, in a very low speed range of the enginerotating speed, the fuel injection rate increases abruptly as therotating speed becomes higher even when the rack position is constant,as shown in FIG. 6. For this reason, even if the rack position is setfor an optimal injection rate at the point A or a at the beginning ofthe starting time, fuel is necessarily injected at an excessively highrate at the point B or b, at which the engine rotating speed becomesequal to N₁. Thus, the conventional starting increase mode entails theproblem of occurrence of misfire due to an increase in the heat ofvaporization taken by the fuel. Further, between B and C or between band c, the rack position is rapidly returned to the ordinary controlposition, so that the fuel injection rate decreases abruptly. Therefore,when the resistance to rotation is large, for example, in the case wherethe temperature of the engine is low, a situation can occur easilywherein the rotating speed cannot be increased as desired because fuelis not sufficiently supplied.

SUMMARY OF THE INVENTION

The present invention has been accomplished to eliminate these drawbacksof the conventional art, and a first object of the present invention isto provide a control method for starting a diesel engine, which makes itpossible to prevent an excessive fuel injection during startinginjection rate increasing. A second object of the present invention isto reliably increase the rotating speed at the time of starting, evenunder a low-temperature engine condition or the like. A further objectof the present invention is to prevent an unnecessary increase in therotating speed of an engine.

To achieve these objects, according to the present invention, there isprovided a control method for starting a diesel engine characterized inthat, between the beginning of the engine starting and a predeterminedfirst engine rotating speed, the control rack is moved in the fuelinjection rate reducing direction so that the rack position has a firstgradient with respect to the engine rotating speed to correct for anincrease in fuel injection rate accompanying an increase in enginerotating speed and, between the first engine rotating speed and a secondengine rotating speed at which the control rack is returned to itsposition for ordinary control, the control rack is moved in the fuelinjection rate reducing direction so that the rack position has a secondgradient greater than the first gradient with respect to the enginerotating speed. It is desirable that the ratio of the difference betweenthe first engine rotating speed and the second engine rotating speed tothe first engine rotating speed is set to a value larger than 20% toincrease the so-called regulation range. Preferably, the position of thecontrol rack, at the beginning of starting the engine, changes betweenpredetermined positions for different increases in the fuel injectionrate according to a temperature of the engine. Further, if thetemperature of the engine is not higher than a predeterminedtemperature, the control rack is moved in the fuel injection ratereducing direction so that the rack position has a predetermined thirdgradient, which is smaller than the second gradient, with respect to theengine rotating speed, from the engine rotating speed at the time whenthe control rack reached a predetermined position during its movementwith the second gradient until the engine rotating speed increases to apredetermined third engine rotating speed which is higher than thesecond engine rotating speed. Alternatively, if the temperature of theengine is not higher than a predetermined temperature, the control rackcan be maintained at a predetermined position, reached by the controlrack during the movement with the second gradient, until the enginerotating speed increases from the engine rotating speed, at the timewhen the control rack reached the predetermined position, to apredetermined third engine rotating speed, which is higher than thesecond engine rotating speed, and the control rack can be moved in thefuel injection rate reducing direction from the third engine rotatingspeed to be returned to its position for ordinary control.

By this arrangement, an increase in the fuel injection rate accompanyingan increase in engine rotating speed is corrected from the beginning ofstarting the engine to the first rotating speed. The increase ininjection rate for starting in the corresponding period can be therebymaintained generally constantly. Occurrence of an excessive increase infuel injection rate is thereby avoided to prevent misfire due to anincrease in heat of vaporization of fuel. Also, an abrupt reduction infuel injection rate is prevented by increasing the so-called regulationrange, so that the necessary amount of fuel for increasing the rotatingspeed can be maintained even if the resistance to rotation is largerunder a low-temperature engine condition or the like. Further, bychanging the increase in fuel injection rate according to thetemperature of the engine at the time of starting, for example, bysetting the position of the control rack on the injection rate reducingside if the engine temperature is high at the time of starting, theinjection of surplus fuel is inhibited when the engine is started in asufficiently warmed condition, thereby preventing generation of blacksmoke. Further, when the engine temperature is not higher than apredetermined temperature, excessive fuel injection can be prevented byincreasing the engine rotating speed to a higher speed with the smallerand gentler third gradient. Therefore, warming-up immediately afterstarting can be suitably performed, so that the engine rotation isstable. In the conventional art, in contrast with the present invention,the engine rotating speed is increased after a change from the startingmode to the ordinary control mode, so that misfire due to an excessiveamount of fuel can occur easily and the engine rotation is unstable, asdescribed above. Warming-up immediately after starting can also besuitably performed by maintaining the control rack at a predeterminedposition if the engine temperature is not higher than a predeterminedtemperature. When the engine temperature is not higher than apredetermined temperature, moving the rack in the injection ratereducing direction or maintaining the rack at a predetermined positionis selected according to starting characteristics of engines.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of an engine controller forcarrying out a control method for starting a diesel engine in accordancewith an embodiment of the present invention;

FIG. 2 is a flowchart for explaining the operation of the controller ofFIG. 1;

FIG. 3 is a graph for explaining a mode of controlling thestarting-increase rack position in accordance with the embodiment;

FIG. 4 is a graph for explaining a rack position control mode withrespect to changes in engine cooling water temperature in accordancewith the embodiment;

FIG. 5 is a graph for explaining a rack position control mode when theengine rotating speed is increased to a higher speed immediately afterstarting in accordance with an applied example;

FIG. 6 is a graph showing an ordinary relationship between the change inengine rotating speed and the fuel injection rate in a case where therack position is constant;

FIG. 7 is a graph showing a mode of controlling the starting-increaserack position in a mechanical governor in accordance with theconventional art; and

FIG. 8 is a graph showing a mode of controlling the starting-increaserack position in an electronic governor in accordance with theconventional art.

BEST MODE FOR CARRYING OUT THE INVENTION

A preferred embodiment of a control method for starting a diesel enginein accordance with the present invention will be described withreference to the accompanying drawings.

FIG. 1 is a block diagram showing an example of an engine controller ofthis embodiment. In this embodiment, which is based on an electronicgovernor, a controller 10 has an ordinary mode output section 12 and astarting increase mode output section 14. The ordinary mode outputsection 12 stores the control rack position of the governor with respectto the engine rotating speed during ordinary control at the time ofhigh-speed rotation, low-speed rotation and the like of an engine 28.The rack positions with respect to the engine rotating speed stored bythe ordinary mode output section 12 is substantially the same as that ofthe conventional control mode. On the other hand, the starting increasemode output section 14 stores the control rack position with respect tothe engine rotating speed when the engine is started.

A control mode of the rack position stored in the starting increase modeoutput section 14 is as indicated by the solid line in FIG. 3. That is,in the rack position control mode of this embodiment, the rack positionat the time a of starting the engine is set at the same position X₀ asin the conventional art. However, while the rack position at a rotatingspeed N₁ (e.g., 300 rpm) is maintained at X₀ in the conventional art,the corresponding rack position is set to X₁ which is on the fuelinjection rate reducing side of X₀, thereby correcting an increase inthe fuel injection rate due to an increase in engine rotating speed, sothat the injection rate can be maintained generally constantly. That is,in the rack position control mode at the time of starting, the rackposition has a predetermined first gradient with respect to the enginerotating speed between the beginning of starting and the rotating speedN₁ as the first engine rotating speed (between a and b₁). The firstgradient is set so that the control rack moves in the injection ratereducing direction as the rotating speed increases, thereby preventingan excessive increase in injection rate which otherwise accompanies anincrease in engine rotating speed.

Subsequently, between b₁ and c₁, when the rotating speed is higher thanN₁, the rack position has a second gradient greater than the firstgradient with respect to the rotating speed, and the rack moves in theinjection rate reducing direction as the rotating speed becomes higher.The starting injection rate increasing is completed at an enginerotating speed N₃ (e.g., 1000 rpm) which is a second engine rotatingspeed. This rotating speed N₃ is increased relative to the rotatingspeed N₂ of the conventional example so that the regulation range islarge. That is, the regulation R of this embodiment is about 230% if therotating speed N₃ is calculated as N₂ in the equation (1) shown above in"Background Art". This value is larger than that of the conventionalexample. This regulation R is set according to engine characteristics, astarting environment and so on, and a value larger than 20% can be usedas the regulation R. Preferably, the upper limit of the regulation R issuch that a rated output is at a rotating speed approximately equal tothe rotating speed N₃. For example, if N₃ is 2000 rpm (rated output),the upper limit is about 600%. Accordingly, a preferable range ofregulation R is 20%<R≦600%. Further, if the efficiency with respect tofuel consumption or the like is a consideration, 30%<R≦300% is morepreferable. The rate of movement of the control rack with respect to theincrease (change) in engine rotating speed is thereby reduced to preventthe fuel injection rate from decreasing abruptly with an increase inrotating speed. Also, the rotating speed of the engine 28 can bereliably increased even if the temperature of the engine is so low thatthe resistance to rotation is considerably large.

The controller 10 is further provided with a water temperaturecorrection circuit 16, a mode selection circuit 18, a deviationcalculation circuit 20, and a proportional integral and differential(PID) control circuit 22 on the output side of the starting increasemode output section 14. The water temperature correction circuit 16 hasrack position correction values corresponding to temperatures of waterfor cooling the engine. The water temperature correction circuit 16corrects the rack position output from the starting increase mode outputsection 14 according to the temperature of the engine cooling water andoutputs the corrected position to the mode selection circuit 18, asdescribed later in detail. The ordinary mode output section 12 isconnected to the mode selection section 18. The mode selection circuit18 outputs the rack position supplied from the ordinary mode outputsection 12 or the water temperature correction circuit 16 to thedeviation calculation circuit 20 according to theexistence/non-existence of a start signal input from a start switch orthe like. The deviation calculation circuit 20 calculates a deviationbetween the control target rack position and the actual rack position.The PID control circuit 22, provided on the output side of the deviationcalculation circuit 20, calculates the amount of operation of anactuator 24 for moving the control rack (not shown) on the basis of asignal outputted from the deviation calculation circuit 20, and operatesthe actuator 24 to adjust the position of the rack.

The control rack moved by the actuator 24 determines the injection rateof an injection pump 26 for injecting fuel into the engine 28. Theposition of the rack is detected by an unillustrated rack positionsensor to be input to the deviation calculation circuit 20 and the modeselection circuit 18. The engine 28 is provided with a water temperaturesensor for detecting the temperature of cooling water and a speed sensorfor detecting the rotating speed of the engine 28 (both not shown). Thecooling water temperature from this cooling water temperature sensor isinputted to the cooling water temperature correction circuit 16, and theengine rotating speed from the speed sensor is inputted to the startingincrease mode output section 14, the mode selection circuit 18 and theordinary mode output section 12. Further, a speed instruction signal isinputted to the ordinary mode output section 12 from a speed instructionoutput section 30 of an acceleration sensor or the like for detectingthe amount of depression of an accelerator pedal.

The diesel engine starting control method using this arrangement ispracticed as described below. First, referring to FIGS. 1 and 2, themode selection circuit 18 is monitoring whether there is a start signalfor engine 28 (starting signal) (Step 41). If there is no start signal,the ordinary control mode is selected (Step 51), and the output signalfrom the ordinary mode output section 12 is supplied to the deviationcalculation circuit 20. On the other hand, when the mode selectioncircuit 18 is supplied with a start signal by turning on the starterswitch or by other means, it stores the start signal in an unillustratedmemory circuit and selects the starting increase mode to enable readingof the output signal from the water temperature correction circuit 16with advancement from Step 41 to Step 42. Also, the mode selectioncircuit 18 reads the rotating speed of the engine 28 outputted from thespeed sensor (Step 43) and makes a determination as to whether thepresent rotating speed is within the range of the starting increase mode(Step 44). If the engine rotating speed is such that the startingincrease mode is required, that is, if the engine speed is not higherthan N₃ shown in FIG. 3, it fetches the output signal from the watertemperature correction circuit 16.

On the other hand, the starting increase mode output section 14 outputsthe rack position X₀ at the beginning of starting (see FIG. 3) andoutputs the control rack position corresponding to the rotating speedfrom the speed sensor to the water temperature correction circuit 16(Step 45).

Next, the water temperature correction circuit 16 reads the temperatureof the engine cooling water that changes according to the temperature ofthe engine 28, corrects the rack position output from the startingincrease mode output section 14, according to the water temperature, andinputs the corrected position to the mode selection circuit 18 (Step46). That is, the water temperature correction circuit 16 has acorrection value table (see FIG. 1) such that, as the temperature of thecooling water of the engine 28 becomes higher, the rack is positioned onthe injection rate reducing side. By using this table, the watertemperature correction circuit 16 corrects the rack position outputtedfrom the starting increase mode output section 14 in the injection ratereducing direction by a correction value corresponding to thetemperature from the water temperature sensor, and outputs the correctedposition to the mode selection circuit 18.

This correction value is determined, for example, on the basis of acooling water temperature of 0° C. The correction value is 0 when thecooling water temperature is equal to or lower than 0° C., and becomesgreater corresponding to the increase in the water temperature above 0°C. The water temperature correction circuit 16 subtracts the correctionvalue from the rack position output from the starting increase modeoutput section 14 to obtain a corrected rack position output. Thecorrected rack position thereby outputted is the same as that outputtedby the starting increase mode output section 14 when the cooling watertemperature is 0° C., as indicated by the solid line in FIG. 4. However,the corrected rack position is as indicated by the dot-dash line whenthe cooling water temperature is 10° C. and as indicated by thedouble-dot-dash line when the cooling water temperature is 20° C.

The corrected rack position, outputted by the water temperaturecorrection circuit 16, is outputted as a rack position instruction tothe deviation calculation circuit 20 by the mode selection circuit 18(Step 47). The deviation calculation circuit 20 calculates a deviationbetween the actual rack position, detected by the rack position sensor,and the rack position from the mode selection circuit 18 (Step 48), andsends this deviation to the PID control circuit 22. The PID controlcircuit 22 drives the actuator according to the magnitude of deviationcalculated by the deviation calculation circuit 20 to adjust the rackposition.

The mode selection circuit 18 also makes a determination based on theoutput signal from the rack position sensor as to whether this positioncoincides with the rack position in accordance with the instruction(Step 49). If they do not coincide with each other, the process returnsto Step 47 and the rack position instruction from the mode selectioncircuit 18 is again outputted to the deviation calculation circuit 20 tocorrect the rack position. When the rack is corrected to the properposition, the process returns to Step 43 and the mode selection circuit18 reads the rotating speed of the engine 28. If it is determined thatthe thus read rotating speed is larger than N₃ and that there is no needfor the starting increase mode, the process moves from Step 44 to Step50 to erase the stored start signal. The ordinary mode is then selectedand the output signal from the ordinary mode output section 12 is readand supplied to the deviation calculation circuit 20 (Step 51). Thedeviation calculation circuit 20 and the PID control circuit 22 controlthe rack position on the basis of a rack position instruction from theordinary mode output section 12 outputted by the mode selection circuit18, as in the case of the starting increase mode described above.

In this embodiment, as described above, as the engine rotating speed isincreased, the rack position corresponding to a condition of the enginerotating at a very low speed changes in the fuel injection rate reducingdirection to correct the increase in fuel injection rate so that thefuel injection rate is generally constant. Occurrence of an unnecessaryhigh injection rate experienced in the conventional art of constantlymaintaining the rack position stationary is thereby reduced, therebymaking it possible to obtain an optimal starting increase in the case ofsmall-orifice injection and to prevent occurrence of misfire due to anincrease in heat of vaporization. Also, the regulation range is extendedto prevent an abrupt reduction in fuel injection rate, so that theinjection rate necessary for increasing the engine rotating speed can bemaintained to reliably increase the rotating speed even if theresistance to the rotation of the engine is large under a low enginetemperature condition or the like. Further, the rack position iscorrected in the injection rate reducing direction according to thelevel of the engine cooling water temperature, thereby enablingprevention of occurrence of black smoke from surplus fuel when theengine, already sufficiently warmed up, is started.

An example of an application of the above-described embodiment will nextbe described with reference to FIG. 5. This applied example relates to acase where the engine rotating speed is increased to a high speed forthe purpose of warming-up or the like immediately after staring theengine. FIG. 5 shows a rack position control mode at the time ofstarting the engine.

In the rack position control mode of this applied example, the controlbetween a and b₁, from the beginning of starting to the engine rotatingspeed N₁, is the same as that of the above-described embodiment, and therack is moved in the reducing direction so that the increase rackposition has the first gradient with respect to the rotating speed. Whenthe engine rotating speed exceeds N₁, the rack is moved in the injectionrate reducing direction (the direction from b₁ to c₁) so that the rackposition has the second gradient, as in the above-described embodiment.During this movement, the rotating speed increases to N₄ (N₄ <N₃) andthe rack moves to the predetermined position X₂ (point d). Thispredetermined position X₂ is, for example, at 30% of the maximum rackmovement position X₀ for starting increase.

After the above-mentioned movement to the point d, the rack is moved inthe injection rate reducing direction so that the rack position has apredetermined third gradient smaller and gentler than the secondgradient with respect to the rotating speed of the engine until theengine rotating speed becomes equal to a rotating speed N₅ (not shown)which is a third engine rotating speed higher than N₃. By this movement,when the rotating speed becomes equal to N₅, the starting increaseposition of the rack is set to 0, thereby completing the rack positioncontrol mode at the time of starting the engine. The control canalternatively be such that, after the above-mentioned movement to thepoint d, the rack position is maintained at the predetermined positionX₂ until the engine rotating speed becomes equal to the abovementionedpredetermined rotating speed N₅, and is moved in the injection ratereducing direction from the rotating speed N₅, and the starting controlis finished at the starting increase position of 0. The selection ofmaintaining the rack position at X₂ or changing the rack position in theinjection rate reducing direction after the above-mentioned movement tothe position d and the setting of the gradient with respect to therotating speed in the case of changing the rack position in theinjection rate reducing direction depend upon characteristics of enginesand are determined as desired by experiment or the like.

By the above-described arrangement, the engine rotating speed isincreased to a higher speed for the purpose of warming-up or the likeafter starting. Therefore, an excessive increase in fuel injection ratecan be limited to prevent occurrence of misfiring and unstable enginerotation due to an increase in heat of evaporation, which effect has notbeen achieved by increasing the engine speed for warming-up or the likeafter a change from the starting increase mode to the ordinary controlmode.

INDUSTRIAL APPLICABILITY

The present invention is useful as a control method for starting adiesel engine, which makes it possible to prevent an excessive increasein fuel injection rate in a low speed rotation range, at the time ofstarting, for prevention of occurrence of misfiring and unstable enginerotation, to reliably increase the rotating speed of the engine at a lowtemperature where the resistance to rotation is large, and to preventoccurrence of black smoke from surplus fuel by controlling the injectionrate according to the engine temperature.

What is claimed is:
 1. A control method for starting a diesel engine,wherein said engine has a control rack for adjusting a rate of fuelinjection into the engine, and wherein said control rack has a setposition for ordinary control of the rate of fuel injection into theengine, said method comprising the steps of:at the time of beginning thestarting of the engine, positioning said control rack at a startingposition on a fuel injection rate increasing side of said set position;moving said control rack from said starting position in the fuelinjection rate reducing direction to a first position, wherein saidfirst position corresponds to a predetermined first engine rotatingspeed, so that the rack position has a predetermined first gradient,with respect to the engine rotating speed, between the beginning ofengine starting and said predetermined first engine rotating speed; andthen moving said control rack from said first position in the fuelinjection rate reducing direction toward a second position, wherein saidsecond position corresponds to a second engine rotating speed at whichsaid control rack is at said set position, so that the rack position hasa predetermined second gradient, with respect to the engine rotatingspeed, between said first engine rotating speed and second enginerotating speed, said second gradient being greater than said firstgradient.
 2. A method in accordance with claim 1, wherein the step ofmoving said control rack from said first position in the fuel injectionrate reducing direction toward a second position comprises moving saidcontrol rack from said first position in the fuel injection ratereducing direction to said set position.
 3. A method in accordance withclaim 1, wherein the step of moving said control rack from said startingposition in the fuel injection rate reducing direction to said firstposition corrects for an increase in fuel injection rate accompanying anincrease in engine rotating speed.
 4. A method in accordance with claim1, wherein a ratio of a difference between said first engine rotatingspeed and said second engine rotating speed to said first enginerotating speed is higher than 20%, when said ratio is expressed as apercentage.
 5. A method in accordance with claim 1, further comprisingthe steps of determining a temperature of the engine, and changing saidstarting position in accordance with the thus determined temperature. 6.A method in accordance with claim 1, further comprising the stepsof:determining a temperature of the engine; if the thus determinedtemperature of the engine is not higher than a predeterminedtemperature, moving said control rack in the fuel injection ratereducing direction from said first position along said second gradientuntil said control rack reaches a predetermined position along saidsecond gradient, and then moving said control rack from saidpredetermined position at a predetermined third gradient with respect tothe engine rotating speed until the engine rotating speed increases to apredetermined third engine rotating speed which is higher than saidsecond engine rotating speed,wherein said third gradient is smaller thansaid second gradient.
 7. A method in accordance with claim 6, whereinthe step of moving said control rack from said starting position in thefuel injection rate reducing direction to said first position correctsfor an increase in fuel injection rate accompanying an increase inengine rotating speed.
 8. A method in accordance with claim 6, wherein aratio of a difference between said first engine rotating speed and saidsecond engine rotating speed to said first engine rotating speed ishigher than 20%, when said ratio is expressed as a percentage.
 9. Amethod in accordance with claim 6, further comprising the step changingsaid starting position in accordance with the thus determinedtemperature.
 10. A method in accordance with claim 1, further comprisingthe steps of:determining a temperature of the engine; and if the thusdetermined temperature of the engine is not higher than a predeterminedtemperature, moving said control rack from said first position in thefuel injection rate reducing direction along said second gradient untilsaid control rack reaches a predetermined position along said secondgradient, and then maintaining said control rack at said predeterminedposition until the engine rotating speed increases to a predeterminedthird engine rotating speed which is higher than said second enginerotating speed.
 11. A method in accordance with claim 10, furthercomprising the step of:returning said control rack to said set positionwhen the engine rotating speed has increased to said third enginerotating speed.
 12. A method in accordance with claim 10, wherein thestep of moving said control rack from said starting position in the fuelinjection rate reducing direction to said first position corrects for anincrease in fuel injection rate accompanying an increase in enginerotating speed.
 13. A method in accordance with claim 10, wherein aratio of a difference between said first engine rotating speed and saidsecond engine rotating speed to said first engine rotating speed ishigher than 20%, when said ratio is expressed as a percentage.
 14. Amethod in accordance with claim 10, further comprising the step ofchanging said starting position in accordance with the thus determinedtemperature.
 15. A control method for starting a diesel engine, whereinsaid engine has a rack for adjusting a rate of fuel injection into theengine, said method comprising the steps of:storing ordinary controlrack positions with respect to engine rotating speed during ordinarymode control for various operating speeds; storing starting control rackpositions with respect to engine rotating speed during starting of theengine; at the time of beginning the starting of the engine providing astart signal, in response to the existence/absence of the start signal,selecting between an ordinary control mode and a starting mode, if theordinary control mode is selected, providing a speed instruction, andpositioning the rack in accordance with the speed instruction and thethus stored ordinary control rack positions; and if the starting mode isselected, positioning the rack in accordance with the thus storedstarting control rack positions, including:positioning the rack at astarting position on a fuel injection rate increasing side of anordinary control rack position; moving said rack from said startingposition in the fuel injection rate reducing direction to a firstposition, wherein said first position corresponds to a predeterminedfirst engine rotating speed, so that the rack position has apredetermined first gradient, with respect to the engine rotating speed,between the beginning of engine starting and said predetermined firstengine rotating speed; and then moving said rack from said firstposition in the fuel injection rate reducing direction toward a secondposition, wherein said second position corresponds to a second enginerotating speed at which said rack is at said set position, so that therack position has a predetermined second gradient, with respect to theengine rotating speed, between said first engine rotating speed andsecond engine rotating speed, said second gradient being greater thansaid first gradient.
 16. A method in accordance with claim 15, whereinsaid starting mode is selected in response to the existence of a startsignal and the ordinary control mode is selected in response to theabsence of a start signal.
 17. A method in accordance with claim 15,further comprising determining a temperature of the engine, correcting athus stored starting control rack position with the thus determinedtemperature to provide a temperature corrected rack position, andwherein said starting mode is selected in response to the existence of astart signal and said temperature corrected rack position.
 18. A methodin accordance with claim 17, where the step of determining a temperatureof the engine comprises sensing a temperature of cooling water for theengine.
 19. Apparatus for operating a diesel engine, said engine havinga rack for controlling a pump for injecting fuel into the engine, saidapparatus comprising:an actuator for adjusting a position of the rack; acontroller having an ordinary mode output section, a starting increasemode output section, a mode selection circuit, and a deviationcalculation circuit; said ordinary mode output section being adapted tostore ordinary control rack positions with respect to engine rotatingspeed during ordinary mode control for various operating speeds; saidstarting increase mode output section being adapted to store startingcontrol rack positions with respect to engine rotating speed duringstarting of the engine; a sensor for providing a speed instruction tosaid ordinary mode output section, a sensor for providing an enginerotational speed signal to each of said ordinary mode output section,said starting increase mode output section, and said mode selectioncircuit; a device for providing a start signal to said mode selectioncircuit at the time of beginning the starting of the engine; a devicefor providing to said deviation calculation circuit a rack positionsignal representative of the actual position of the rack; wherebyresponsive to the existence/absence of said start signal said modeselection circuit selects a signal responsive to an output of saidordinary mode output section or a signal responsive to an output of saidstarting increase mode output section and outputs the thus selectedsignal to said deviation calculation circuit; whereby the deviationcalculation circuit determines a difference between a rack positionrepresented by the thus selected signal and the actual rack positionrepresented by the rack position signal; wherein the actuator iscontrolled responsive to the thus determined difference; and wherein atthe time of beginning the starting of the engine, said starting increasemode output section provides an output signal for positioning said rackat a starting position on a fuel injection rate increasing side of anordinary control rack position, and then for moving said rack from saidstarting position in the fuel injection rate reducing direction to afirst position, wherein said first position corresponds to apredetermined first engine rotating speed, so that the rack position hasa predetermined first gradient, with respect to the engine rotatingspeed, between the beginning of engine starting and said predeterminedfirst engine rotating speed, then for moving said rack from said firstposition in the fuel injection rate reducing direction toward a secondposition, wherein said second position corresponds to a second enginerotating speed at which said rack is at an ordinary control rackposition, so that the rack position has a predetermined second gradient,with respect to the engine rotating speed, between said first enginerotating speed and second engine rotating speed, said second gradientbeing greater than said first gradient.
 20. Apparatus in accordance withclaim 19, further comprising a temperature correction circuit forreceiving a signal from the starting increase mode output section andproviding a temperature corrected signal to said mode selection circuitas said signal responsive to an output of said starting increase modeoutput section, and a sensor for determining a temperature of the engineand for applying a temperature signal to the temperature correctioncircuit.